4.3 How can I completely wipe all data from disk drives before they are sold?

The "formatvol" command within the VOLUTIL utility should reformat disks that are not mounted within a volume set. The command does take a while to complete. And, don't interrupt the "formatvol" command - unless you really want the disk to be inaccessable. Depending upon the size and model of disk, the process could take 2 or 3 hours to complete.